2000 Ford Ranger Overheating Mystery?

My son's 2000 Ford Ranger, 3.0 V6 overheats. We have replaced everything (that we know of) except putting in a new engine. It started about a year ago when it overheated. Took it to our trusty mechanic shop. They replaced the radiator and thermostat. After it overheated again, my son replaced the water pump and the problem persisted. The mechanic then suggested it might have a bad head gasket. The mechanic put some Stop leak in as a temporary fix. It turned out to be drivable IF the truck was warmed up enough to open the thermostat (had to wait for the gauge to go up and then drop down and then level out in the correct spot). If you tried to drive it without a warm up, it would overheat as soon as the thermostat opened. Also, a low temp thermostat was put in. A couple of months ago it overheated after shutting off the engine (water and lots of bubbling noise came from the overflow reservoir. My son decided to change the head gaskets. The heads were resurfaced, new seals, exhaust valve seats and all looked good. The thermostat was again replaced. New coolant in place and it was ready to test drive. The truck was driven for about a half an hour from a cold start.. It didn't overheat. Thinking we've fixed it, my son takes it out, stops by a friends house about a mile away to pick something up. He leaves the truck running and when he comes back out about 5 minutes later the gauge is pegged. At that point, the following parts were changed - radiator, fan clutch, coolant temp sensor, thermostat, upper radiator hose, and sensor elbow.



Again parts replaced and repaired since the first overheat include:

2 radiators

1 water pump

1 coolant temp sensor

1 elbow (coolant sensor attaches to it)

1 elbow (attaches to the smaller hose of the lower radiator hose)

6 thermostats

2 fan clutches

2 sets of upper and lower radiator hoses

Head gaskets and complete seal/gasket kit

Heads resurfaced and fixed with new exhaust valve seats

Head bolts and header bolts

2 Radiator caps



We're out of ideas and need some help. Many thanks, in advance, if you've had a similar, resolved problem or think you might know what's going on.
2000 Ford Ranger Overheating Mystery?
Ok, was the head gaskets put on the correct way, they are have the words FRONT wrote on them and easy to over look unless you know they are there, if installed backwards then you may have fixed 1 problem only to creat another. I have seen this happen before and is an easy mistake to do. 1 Gasket will have FRONT and you will see the words at the front of the motor, the other side will be turned over so the FRONT is still at the front just flipped upside down
2000 Ford Ranger Overheating Mystery?
Have you replaced the bottom radiator hose? A soft hose can be sucked flat by the water pump %26amp; stop water circulation. After everything cools down, the hose pops back open %26amp; looks fine. That's why some bottom hoses have like a steel coil spring inside them.
Hate to tell you this, but it's east to check for head gasket failure/ cracked head- pull the plugs, look at the business end for rust, any time it's been overheated then sat for a few days- you can also sniff for anti-freeze

Couldn't find a good picture, but there should be a place to %26quot;burp%26quot; excess air out of the engine- usually located right in front, either On, or right behind, the outlet/thermostat housing-looks like either a bolt with no purpose, or it might look like a brake bleeder,either way, if an air pocket stays in the top of the engine, it'll stay there, and get HUNDREDS of degrees hotter than the water !

To burp it, run it for just a couple minutes, shut her down, wait for water to get heat from engine- maybe 5 minutes-then open the valve, close when no more air comes out-just water.

*** you might have to do this 2 or 3 times to get all the air!
Has an automotive technician ever verified if there are actually any exhaust gases present in the radiator/cooling system? This can be done either with a chemical method %26quot;Block Check%26quot; or with an exhaust analyzer which will measure the presence of unburned hydrocarbons in the coolant. Are you using factory replacement parts or after market parts? There are no known overheating problems with the Ranger 3.0L engine, and the radiator is a single row design with no HD version with 2 rows available.

Do you run a 50/50 mix of the correct coolant/water? Running 100% coolant can cause the engine to overheat. What thermostat are you running, does it have an air bleed passage? we used to drill a small bleed hole to prevent trapped air behind the stat.